The present disclosure relates to a method for transferring batteries, for example lithium-ion batteries, to a discharged state. Furthermore, the present disclosure relates to a battery management system for a battery system, an inverter, a system for generating an AC voltage and a charging current source. Furthermore, the present disclosure relates to a motor vehicle.
High-power battery systems for generating AC voltage often comprise a battery based on lithium-ion technology and an inverter having power switches arranged in series on parallel current branches. If the inverter of such a battery system comprises three or more parallel current paths, then the battery system can be embodied directly for supplying a machine suitable for generating torque for the driving of hybrid and electric vehicles. Such battery systems are also designated as traction battery systems or as traction batteries for short.
In order to obtain the power and energy data required in hybrid and electric vehicles and in other AC voltage-based applications, batteries have electrical voltages of up to 450 volts. In traction batteries, for this purpose, individual battery cells are connected in series and in part additionally in parallel.
In high-power batteries, therefore, an electrical voltage limit of 60 volts which is classified as non-critical with regard to contact by humans, is usually exceeded.
The basic circuit diagram of a battery 220 according to the prior art is illustrated in FIG. 1. Alongside the battery cells 140, the battery 220 also has a so-called charging and disconnecting device 130, which in FIG. 1 is arranged between the positive pole 100 of the battery 220 and the positive pole of the battery cells 140. By means of a disconnecting switch 120 and a disconnecting switch 125, a positive pole of the battery cells 140 can be electrically disconnected from the positive pole 100 of the battery 220. By means of the disconnecting switch 120, the positive pole of the battery cells 140 can also be electrically connected to the positive pole 100 of the battery 220 with low impedance, in other words with low resistance. With the disconnecting switch 120 open, the positive pole of the battery cells 140 can also be electrically connected to the positive pole 100 of the battery 220 via a charging current source 110 by means of the disconnecting switch 125. As an optional functional unit, a further disconnecting device 170 is illustrated in FIG. 1, by means of which the battery cells 140, if required, can be disconnected from the negative pole 160 of the battery 220 in a two-pole manner via a second disconnecting switch 150.
FIG. 2 illustrates the basic circuit diagram of an electrical drive system according to the prior art, as is used for example in electric and hybrid vehicles. The electric machine 200, which is embodied as a polyphase machine, for example, is supplied via an inverter or pulse-controlled inverter 210.
In the case of the battery systems currently known it is customary that in the event of a critical state being identified, such as an accident, for example, in which the restraint systems are triggered, the battery is disconnected from the on-board traction power supply system of the vehicle. If possible by virtue of two disconnecting devices being present, two-pole disconnection from the inverter is effected in this case.
WO002009011749A1 discloses a method for inhibiting the propagation of thermal events in an energy storage system having a multiplicity of cells. The method comprises the steps of identifying heat sources in the energy storage system and in the multiplicity of cells, detecting the presence of specific predefined states of the energy storage system, and performing a previously defined action if one of the previously defined states has been detected.